The present invention relates in general to circulatory assist devices, and, more specifically, to preventing contamination of the surgical field during an implantation procedure while avoiding the need to sterilize an external control unit.
Many types of circulatory assist devices are available for either short term or long term support for patients having cardiovascular disease. For example, a heart pump system known as a left ventricular assist device (LVAD) can provide long term patient support with an implantable pump associated with an externally-worn pump control unit and batteries. The LVAD improves circulation throughout the body by assisting the left side of the heart in pumping blood. One such system is the DuraHeart® LVAS system made by Terumo Heart, Inc., of Ann Arbor, Mich. The DuraHeart® system employs a centrifugal pump with a magnetically levitated impeller to pump blood from the left ventricle to the aorta. An electric motor magnetically coupled to the impeller is driven at a speed appropriate to obtain the desired blood flow through the pump.
A typical cardiac assist system includes a pumping unit, electrical motor (e.g., a brushless DC motor integrated in the pump housing), drive electronics, microprocessor control unit, and an energy source such as rechargeable batteries and/or an AC power conditioning circuit. The system is implanted during a surgical procedure in which a centrifugal pump is placed in the patient's chest. An inflow conduit is pierced into the left ventricle to supply blood to the pump. One end of an outflow conduit is mechanically fitted to the pump outlet and the other end is surgically attached to the patient's ascending aorta by anastomosis. A percutaneous cable connects to the pump, exits the patient through an incision, and connects to the external control unit. For practical reasons, it is preferable that the percutaneous cable extends for only a short distance from the incision. A cable connector is provided at the end of the percutaneous cable in order to connect with an extension cable coming from the external controller.
As in any surgical procedure, it is necessary to maintain sterility within a sterile field during implantation of the LVAD. Sterility is required not only for the region around the surgical incisions and the components being implanted, but also for any objects entering or partially entering the field.
In the event of any problems or failure of the external control unit, it may become necessary to replace it. Therefore, a removable connection between the control unit and the percutaneous cable is employed. When the removable connection is provided at the connection between the percutaneous cable and the extension cable from the external unit (i.e., the extension cable is permanently fixed to the external control unit), then the control unit itself must be sterilized for the implantation procedure. In order for the control unit to be sterilizable, it must be airtight. Therefore, making a sterilizable control unit undesirably increases the cost of manufacture.
Alternatively, a make/break connection between the control unit and the extension cable may be provided such that the control unit does not enter the sterile field during implantation. If the extension cable is fully sterilized but extends outside the sterile field in order to be connected with the control unit outside the sterile field, then safety is maintained. However, the resulting system has a configuration subject to the disadvantage that in the event that it later becomes necessary to replace the control unit then there are two breakable connections to deal with (i.e., at either end of the extension cable). The possibility of two different connections can be confusing to users during an exchange of control units. It is desirable that only one possible disconnection/reconnection should be presented to the user when making such an exchange.